Process for Reducing Unsaturated Hydrocarbons in Aromatic Fraction Through Selective Hydrogenation

Abstract

Disclosed are a process and system that are capable of performing selective hydrogenation on aromatic fractions by configuring a catalyst bed through staged loading of a plurality of hydrogenation catalysts with different catalytic properties, or configuring a catalyst system in which a plurality of hydrogenation catalysts are arranged using a plurality of reactors in such a way as to be equivalent with the staged loading, and as a result, are capable of suppressing aromatic loss while improving the selective removal of unsaturated hydrocarbons in the aromatic fraction and durability compared to the case of using a single catalyst.

What is claimed is: 
     
         1 . A system for separating and purifying aromatic hydrocarbons, which comprises:
 a feed line of an aromatic hydrocarbon-containing feedstock having a bromine index of at least 30;   a hydrogen feed line;   a hydrogenation reactor communicating with each of the feed line of the feedstock and the hydrogen feed line, the hydrogenation reactor filled with a multi-stage catalyst bed, in which the multi-stage catalyst bed comprises a first catalyst bed comprising at least one stage and at least one second catalyst bed disposed at the downstream of the first catalyst bed along a flow direction of the feedstock transferred through the feed line; and   at least one separator communicating with the hydrogenation reactor, the separator separating a product containing at least one aromatic hydrocarbon selected from the group consisting of C6 aromatics, C7 aromatics, C8 aromatics and C9+ aromatics, among products discharged from the hydrogenation reactor,   wherein,   the first catalyst bed comprises a support containing inorganic oxide, and at least one active metal selected from the group consisting of Ni, Pd, Pt, Ru, Re, Co, Mo, Co—Mo, Ni—Mo, and Ni—W, in which, among the active metals, each of Re, Co, Mo, and Co—Mo is a reduced or sulfide form, and each of Ni, Pd, Pt, Ru, Ni—Mo and Ni—W is a sulfide form, and   the second catalyst bed comprises a support containing inorganic oxide, and Ni—Mo and/or Ni—W in a reduced form as an active metal.   
     
     
         2 . The system according to  claim 1 , wherein the hydrogenation reactor is configured such that at least 30% by weight of unsaturated hydrocarbons in the aromatic hydrocarbon-containing feedstock is removed by hydrogenation. 
     
     
         3 . The system according to  claim 1 , wherein an aromatic loss in the product is less than 1% by weight relative to the aromatic hydrocarbon-containing feedstock. 
     
     
         4 . The system according to  claim 1 , further comprising a transalkylation unit for converting a fraction containing C6 aromatics, C7 aromatics and/or C9+ aromatics among the product separated from the at least one separator, into C8 aromatics. 
     
     
         5 . The system according to  claim 4 , further comprising a recycling line for recycling unrecovered C8 aromatics after separating and recovering para-xylene from the C8 aromatics. 
     
     
         6 . The system according to  claim 1 , further comprising a para-xylene separation and/or recovery unit for separating and/or recovering para-xylene from the C8 aromatics among the product separated from the at least one separator; and
 a xylene isomerization unit for isomerizing unseparated/unrecovered C8 aromatics, other than the para-xylene to form an increased content of para-xylene.   
     
     
         7 . The system according to  claim 6 , further comprising a recycling line for recycling the remaining xylene fraction after separating and/or recovering para-xylene among the aromatic fraction discharged from the xylene isomerization unit. 
     
     
         8 . The system according to  claim 1 , wherein the inorganic oxide comprises at least one selected from the group consisting of alumina, silica, silica-alumina, aluminum phosphate, zirconia, titania, bentonite, kaolin, clinoptilolite and montmorillonite. 
     
     
         9 . The system according to  claim 1 , wherein an amount of the at least one first catalyst bed is in a range of 10% to 90%, based on the total volume of the at least one first catalyst bed and the second catalyst bed. 
     
     
         10 . The system according to  claim 1 , wherein the support in each of the at least one first catalyst bed and the second catalyst bed is in a shape of cylinder, granule, pellet, tablet, or sphere. 
     
     
         11 . A system for separating and purifying aromatic hydrocarbons, which comprises:
 a feed line of an aromatic hydrocarbon-containing feedstock having a bromine index of at least 30;   a hydrogen feed line;   a multi-stage hydrogenation unit communicating with each of the feed line of the feedstock and the hydrogen feed line, in which the multi-stage hydrogenation unit comprises a first reaction unit containing at least one first catalyst and a second reaction unit communicating with the first reaction unit at the downstream of the first reaction unit and containing a second catalyst along a flow direction of the feedstock transferred through the feed line; and   at least one separator communicating with the multi-stage hydrogenation unit, the separator separating a product containing at least one aromatic hydrocarbon selected from the group consisting of C6 aromatics, C7 aromatics, C8 aromatics, and C9+ aromatics, among products discharged from the multi-stage hydrogenation unit,   wherein,   the first catalyst comprises a support containing inorganic oxide, and at least one active metal selected from the group consisting of Ni, Pd, Pt, Ru, Re, Co, Mo, Co—Mo, Ni—Mo, and Ni—W, in which, among the active metals, each of Re, Co, Mo, and Co—Mo is a reduced or sulfide form, and each of Ni, Pd, Pt, Ru, Ni—Mo and Ni—W is a sulfide form, and   the second catalyst comprises a support containing inorganic oxide, and Ni—Mo and/or Ni—W in a reduced form as an active metal.   
     
     
         12 . The system according to  claim 11 , wherein the multi-stage hydrogenation unit is configured such that at least 30% by weight of unsaturated hydrocarbons in the aromatic hydrocarbon-containing feedstock is removed by hydrogenation. 
     
     
         13 . The system according to  claim 11 , wherein an aromatic loss in the product is less than 1% by weight relative to the aromatic hydrocarbon-containing feedstock. 
     
     
         14 . The system according to  claim 11 , further comprising a transalkylation unit for converting a fraction containing C6 aromatics, C7 aromatics and/or C9+ aromatics, among the product separated from the at least one separator, into C8 aromatics. 
     
     
         15 . The system according to  claim 14 , further comprising a recycling line for recycling unrecovered C8 aromatics after separating and recovering para-xylene from the C8 aromatic hydrocarbon-containing product. 
     
     
         16 . The system according to  claim 11 , further comprising a para-xylene separation and/or recovery unit for separating and/or recovering para-xylene from the C8 aromatics among the product separated from the at least one separator; and
 a xylene isomerization unit for isomerizing unseparated/unrecovered C8 aromatics, other than the para-xylene to form an increased content of para-xylene.   
     
     
         17 . The system according to  claim 16 , further comprising a recycling line for recycling the remaining xylene fraction after separating and/or recovering para-xylene among the aromatic fraction discharged from the xylene isomerization unit. 
     
     
         18 . The system according to  claim 11 , wherein the inorganic oxide comprises at least one selected from the group consisting of alumina, silica, silica-alumina, aluminum phosphate, zirconia, titania, bentonite, kaolin, clinoptilolite and montmorillonite. 
     
     
         19 . The system according to  claim 11 , wherein the support in each of the at least one first catalyst and the second catalyst is in a shape of cylinder, granule, pellet, tablet, or sphere. 
     
     
         20 . The system according to  claim 11 , wherein the first reaction unit comprises a plurality of reactors connected in series.